go/oasis-test-runner: Fix e2e/consensus-state-sync scenario

[kostko]

Instead of terminating the validator-to-be-synced immediately and restarting
it later, do not even start it. Early stopping could result in state that
prevents proper state sync later.

[codecov]

Codecov Report

Merging #3194 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3194      +/-   ##
==========================================
- Coverage   67.92%   67.88%   -0.05%     
==========================================
  Files         380      380              
  Lines       36627    36627              
==========================================
- Hits        24879    24863      -16     
- Misses       8525     8594      +69     
+ Partials     3223     3170      -53     

Impacted Files	Coverage Δ
go/consensus/tendermint/full/statesync.go	0.00% <0.00%> (-64.07%)	⬇️
go/consensus/tendermint/light/client.go	0.00% <0.00%> (-46.35%)	⬇️
go/storage/mkvs/checkpoint/checkpoint.go	86.66% <0.00%> (-13.34%)	⬇️
go/consensus/tendermint/api/api.go	77.65% <0.00%> (-9.58%)	⬇️
go/common/grpc/policy/policy.go	64.38% <0.00%> (-6.85%)	⬇️
go/storage/api/root_cache.go	74.60% <0.00%> (-6.35%)	⬇️
go/consensus/tendermint/abci/mux.go	54.88% <0.00%> (-5.06%)	⬇️
go/storage/metrics.go	81.08% <0.00%> (-4.06%)	⬇️
go/storage/mkvs/tree.go	89.28% <0.00%> (-3.58%)	⬇️
go/storage/mkvs/insert.go	87.75% <0.00%> (-2.73%)	⬇️
... and 28 more

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